This invention relates to a coding method for efficient transmission or storage of a binary signal, such as a two-level facsimile signal.
Heretofore, there have been proposed, as two-level facsimile signal coding systems, (1) a run-length coding system in which a signal obtained by scanning is converted into a time series train and then the magnitudes of the run lengths of white and black are successively coded alternately with each other for transmission and (2) a system in which signals of plural, for example, two scanning lines are simultaneously coded all together. The system (1) does not utilize at all the property that facsimile signals have a high correlation in a direction perpendicular (vertical) to the scanning line direction; therefore, the compression efficiency is low. The system (2) makes use of the correlation in the vertical direction with respect to the signals of several scanning lines to be coded at a time but does not utilize the correlation to signals of other scanning lines; consequently, the compression effect is higher than that in the case of the system (1) but not sufficient.